(1) Matzah that is mixed with liquid during cooking; avoided by scrupulously observant because of the possibility that unbaked flour in the matzah could be exposed to the liquid and thereby become chametz, forbidden during Passover.

Not to speak of on Shabbat (used when a subject is not suitable for the Holy Shabbat, primarily business and money manners, to indicate that one shouldn't discuss it). Usually followed by a short comment about the "forbidden" subject.